[Seroprevalence of bactericidal anti-meningococcal antibodies in Cantabria 10 months following a vaccination campaign].

BACKGROUND

The Self Governing Region of Cantabria within the state of Spain has a population of 541,885, of which 107,787 individuals are aged from 18 months to 19 years. A vaccination campaign against meningitis was conducted in this Region in February and March, 1997. It was directed at children from the age of 18 months up to 19 years old, and included all municipal areas, achieving a coverage of more than 95%. In the following 12 months the efficacy achieved by the vaccination was 95.68% for all age groups. To help decide on the need for re-vaccination, a study of the prevalence in serum of bactericide antibodies in the vaccinated population was carried out.

METHODS

In December 1997 blood samples from 414 vaccinated children were analysed, obtained at random in opportunist sampling in First-Aid Centres and Public Hospitals within this Region, as well as from children in public kindergartens run by the General Board of Social Well-Being in Cantabria. The number of bactericide antibodies was analysed in the National Centre for Microbiology, and the level of "vaccination effect" was set at a dilution of 1/8.

RESULTS

The following percentages of titres > or = 1/8 were obtained (the age groups of school pupils are shown in brackets): 0% (18-24 months old), 4% (1.5-4 years old), 7.1% (1.5 to 6 years old), 51.3% (6 to 12 years old). Due to the fact that the definition of the "vaccine effect" was artificially set at a dilution of 1/8, while other studies set it at a dilution of 1/4, in 287 serum samples with a result of < 1/8 the bactericide assay was repeated with a dilution of 1/4, with the result that 286 (99.6%) were negative. I.e., the final result does not vary if we set the cut-off point at 1/4 instead of 1/8. No significant differences were found due to whether or not the samples came from children in municipalities where there had been cases of meningitis C.

CONCLUSIONS

Bactericide activity is very low in those children aged less than 4-6 years old, and is less than has been published, although it is greater above this age. This contrasts with the excellent clinical-epidemiological results, as there was no case amongst the least serologically "protected" population, in spite of the fact that meningococcus C remains in circulation in Cantabria, within the population that was not targeted by the campaign.